The present invention relates to a color signal processing circuit for use in color television receivers.
In the present color television systems used in the world, a carrier chrominance signal is multiplexed with a luminance signal to produce a composite color video signal. A color subcarrier frequency is selected to a high frequency (3.58 MHz in the NTSC system) in the frequency band of the luminance signal and the bandwidth of color signals for amplitude-modulating the color subcarrier is considerably narrow as compared with that of the luminance signal.
The composite color video signal is separated in the color television receiver to the carrier chrominance signal and the luminance signal, and the carrier chrominance signal is applied to a color demodulation device where the color signals are recovered from the carrier chrominance signal. The recovered color signals are applied to the color cathode-ray tube. It is well known that cross-color disturbance generates color noises in a color picture when high frequency components of the luminance signal leak into the signal transmission path of the carrier chrominance signal applied to the color demodulation device. As described above, the bandwidth (0 to 500 kHz in the NTSC system) of color signals is considerably narrow as compared with that of luminance signal, and color-fringing components are, therefore, liable to be generated at front and back ends of color signals when produced at broadcasting stations. The color-fringing components are not eliminated at broadcasting stations and modulate, together with pure color signals, the color subcarrier. Accordingly, color-fringing is possibly caused at boundaries of objects in the reproduced picture at the receiving side and appears noticeably at a boundary between colored portion and white portion in the picture.
Cross-color disturbance appears in various forms on the screen. In a picture shown in FIG. 1 and including black, white and color portions B, W and C, for example, cross-color disturbance appears at boundaries X1 and X2 between black portion B and white portion W, boundary X3 between black portion B and colored portion C, and boundary X4 between colored portion C and white portion W. This is because the level of luminance signal changes abruptly at boundaries X1, X2, X3 and X4 and thus high frequency components of luminance signal leak into carrier chrominance signal.
Color-fringing is also caused at boundary X3 between black and color portions B and C and at boundary X4 between color and white portions C and W. This is because the carrier chrominance signal transmitted by broadcasting station already includes the color-fringing components, and the color signals recovered from the carrier chrominance signal cannot fade out abruptly at boundaries X3 and X4 to thereby intrude into black and white portions B and W. Color-fringing is visibly noticeable at the boundary X4 between color and white portions C and W.